The present invention relates to a method for the detection and elimination of foreign bodies in a flow of tobacco.
In particular, the present invention relates to a method of detecting and eliminating foreign bodies such as might be contained within a flow of filler material used conventionally in the manufacture of tobacco products.
The invention finds application, advantageously, in the art field concerned with the detection of non-metallic foreign matter that may be present either in a ribbon of loose tobacco filler or in a continuous cigarette rod.
Foreign bodies present within a flow of shredded tobacco filler, destined for use in the manufacture of tobacco products, can be harmful to the smoker in that when burned they may give off toxic or at all events disagreeable substances. It is therefore particularly important that tobacco products should not contain these foreign bodies.
Foreign matter of a ferrous nature is removed normally from a mass of shredded tobacco by causing a flow of the tobacco, however ordered, to advance along a path passing close to a magnet.
Other foreign matter including metallic materials can be detected utilizing infrared rays or other types of electromagnetic radiation, directed in such a manner that the radiated energy is impeded, diverted or reflected by the metallic foreign body.
Satisfactory results have also been achieved in the detection of non-metallic foreign bodies using beta or gamma rays, albeit with the drawback that these are generated by a radioactive and therefore potentially hazardous source.
As an alternative to these types of radiation, the prior art also embraces the use of devices as disclosed in Italian patent no 1 286 764, designed to emit electromagnetic radiation in the infrared range and equipped with special filters, which are able to generate different beams of electromagnetic radiation with wavelengths selected according to the particular type of foreign body being detected (wood, plastic, glass, etc.).
The method in question has been found unreliable however, inasmuch as these types of electromagnetic radiation appear to be influenced by the physical properties of the tobacco, for example the length and color of the fibers.
The object of the present invention is to provide a method of detection and rejection unaffected by the aforementioned drawbacks.